1. Field of the Invention
The present invention is related to machine control systems in general and computerized numerical control systems for machine control in particular.
2. Prior Art
Numerical control systems ae used to control machines such as machine tools. Digital commands are input with a punched tape to describe the part to be cut on a machine such as a milling machine. These commands are accessed by the numerical control system and are executed to drive the machine to automatically cut the part.
Prior art numerical control systems have been designed around special purpose digital devices where operations such as logic, control, and computations are performed with special purpose logic. Because of the high cost and limited capability of these special purpose numerical control systems, most of the computations are preprocessed with a remote, large scale computer using a parts program compiler such as APT. The remote computer preprocesses the information and generates a punched tap in a control oriented language containing the initial conditions and commands required by the special purpose numerical control equipment. These parts program tapes describe the part to be generated and are used as the command inputs to the numerical control system to cut the part. Tape program errors are common, requiring test runs to isolate and correct these errors. When a test run is completed, the parts programmer provides corrections to the remote computer in a compiler oriented language to generate a corrected tape. Turn-around time for a new tape is often twenty four hours and it is common for five corrected tapes to be required before an acceptable production tape is generated. Therefore, a week of parts program checkout time can be required prior to starting production. An expensive numerical control system can therefore be tied up waiting for a production tape to be checked-out and regenerated. In addition, excessive expense can be incurred for repeated use of the remote large scale APT program computer. Other problems and expenses are incurred associated with the uncertainty of when a production tape will be available and the expensive delays in production start up.
In order to simplify programming of complex parts, various parts programming compilers have been developed. The APT compiler is the most common of these parts programming compilers. It is serviced by the Illinois Institute of Technology Research Institute (IITRI) which provides documentation, services, and software for this parts prgram compiler.
An attempt has been made to circumvent the tape correction problems by providing a remote large scale computer operating in a time-shared mode to provide rapid correction of parts programs. In such a system, the remote computer is located in the plant containing the machines and provides storage for the parts programs for many numerical control systems in that plant. In operation, this central computer will transmit a new block of commands to each special purpose numerical control system when the prior block of commands has been executed. When the parts programmer detects an error, he will stop the operation of the numerical control system and enter a correction, which will be transmitted to the remote computer. This correction is made in a compiler oriented language which is acceptable by a large scale computer containing a parts program compiler such as APT. The remote computer will compile a new program, convert it to a control oriented language such as the EIA standard format, then make this corrected parts program available to the special purpose numerical control system for continued operation. Such systems using a remote computer in conjunction with special purpose, non-computerized numerical control systems at every machine are typified by the Sundstrand Omnicontrol and the General Electric Commander systems.
Excessive expenses are incurred with the requirements for these remote computers generating control oriented commands for various non-computerized numerical control systems located at the machine being controlled. In addition, the capabilities of each numerical control system is still limited by the non-computerized numerical control, where the remote larger scale computer can't adequately service all numerical control systems in the shop with any more than parts program modification and superficial preprocessing operations.
The limited capability of the prior art, non-computerized numerical control systems has placed a considerable burden on the parts programmer, system operator, and the entire manufacturing organization. In prior art systems; parts programming requires many unnecessary calculations, workpiece setup and equipment operation are complex, and manufacturing control is very limited. Other problems are encountered due to the limitations of the prior art numerical control systems.